A first prior art steam peeler is shown in FIG. 1, in an initial product loaded disposition, in which a generally cylindrical pressure vessel 101 is oriented with its axis at an oblique upward angle relative to the horizontal, for loading 102 of product 103 through the mouth 104 of the vessel 101 into an internal cage 119 rotatably mounted within vessel 101. Deaeration is then effected, the pressure vessel 101 is closed, and steam is blown in 105. The pressure vessel 101 is then rotated about an axis perpendicular to the plane of the paper into a disposition in which its axis of symmetry extends substantially horizontally and in the plane of the paper, at which stage the cage 119 is rotated within the vessel 101 about that axis of symmetry to effect the required peeling action while the vessel 101 remains charged with steam under pressure. The pressure within the vessel 101 is then relieved by rapid discharge of the steam, so that the peel is detached from the product, following which pivoting of the pressure vessel 101 about the axis perpendicular to the plane of the paper is again effected, to bring the mouth 104 of the vessel 101 into a downward disposition in which the axis of symmetry of the vessel 101 is oriented at an acute angle with respect to the horizontal, but below the horizontal as compared with the disposition shown in the drawing, at which stage the product 103 is discharged from the pressure vessel 101. The structure is technically complex, because of the diversity of pivoting and rotational movements required, together with the necessity to be able to admit and discharge steam under pressure at various different stages in the sequence of movements, as well as closing the vessel 101 and maintaining it in a sealed condition during the operational cycles.
In FIG. 2, a second form of rotatable steam peeling pressure vessel 201 is shown. In this arrangement, the vessel 201 is rotatable about an axis again perpendicular to the plane of the paper and is initially oriented in a disposition in which its axis of general symmetry 208 is disposed vertically upwards for product charging, 202 through mouth 204, as shown in the drawing. The loading and discharge opening 204 of the pressure vessel 201 is sealed by means of a door 206 which closes from the interior, thereby limiting the extent to which the pressure vessel 201 can be filled with product 203, in that the door 206 closing path of movement must be clear of product 203 during closing and opening movements. During steam peeling, rotation takes place by the pressure vessel 201 being turned about the axis perpendicular to the plane of the paper. By contrast with the arrangement of FIG. 1, rotation of the pressure vessel 201 is provided only about one axis, rather than the two degree of freedom arrangement provided by the structure of FIG. 1. There is no rotation about the axis of symmetry 208 of the pressure vessel 201. On completion of the pressurised steaming period, the vessel 201 is returned to the upright orientation shown in the drawing, pressure is released, and condensate may drain away at the base 211 of the pressure vessel 201 where the product is supported on a grid 213. When pressure is released, the door or inwardly opening lid 206 may also be opened, following which the pressure vessel 201 is inverted or substantially inverted for product 203 discharge. Disadvantages of the arrangement include the necessity for the pressure vessel 201 to be restored to an orientation in an upward direction for opening and closing of the door 206, while also the necessity to provide for drain of condensate arises out of a relatively slow reduction in pressure being applied in the system of FIG. 2, so that condensate forms within the pressure vessel 201, as compared with systems in which rapid flash or high-speed exhaust of the pressurised steam is provided, where formation of condensate within the pressure vessel is substantially minimized.
In the third prior art arrangement in which a rotating pressure vessel is used, as shown in FIG. 3, the pressure vessel 301 is mounted for rotation about a substantially horizontal axis 307 extending in the plane of the paper of the drawing. The pressure vessel 301 is however mounted on this axis 307 in a skewed or canted manner, so that its general axis of symmetry 308 at all times defines an acute angle with respect to the axis 307 of rotation. Charging 302 of the pressure vessel 301 takes place in the manner previously described with the opening 304 of the pressure vessel 301 being upwardly directed, and discharge takes place when the pressure vessel 301 is turned so that the opening 304 is directed downwardly. When the pressure vessel 301 is loaded and sealed by closure of the vessel door, it is charged 305 with steam and is rotated about the horizontal axis 307, but remains in its canted or skewed disposition with respect to this axis 307 at all times. Again in this structure, there is no rotation about the axis of symmetry 308. Because of the canted or skewed arrangement of the pressure vessel 301, the construction is required to tolerate and withstand substantial out of balance forces during rotation of the pressure vessel 301, thereby necessitating a particularly robust and heavy supporting structure. Feed of product to the pressure vessel is effected by means of a weighing conveyor and associated ducting or a hopper arrangement 302, as applies also to the prior art apparatus of FIG. 1 and may likewise be associated with the system of FIG. 2. Exhaust is effected as indicated by reference numerals 314.
FIG. 4 shows a first prior art arrangement using a static pressure vessel 401 which is equipped with a product inlet door 406 at the top 404 and a product outlet door 409 at the bottom 411. Within the static pressure vessel 401, there is provided a continuously rotating agitator 412 and a condensate-separating grid 413. Fixed connections provide for steam supply 405 and exhaust 414 and for condensate discharge 415, all substantially automatically controlled during operation of the system. After filling 402, product 403 to be peeled is held in the compartment 416 above the grid 413, while the agitator 412 keeps the product 403 moving, but without product damage. Separation of condensate, which forms in this system, is continuous throughout the steam exposure time, because of the rotational agitation that is effected about an axis 408 inclined relative to the horizontal. Condensate flows away through the grid 413 and is evacuated by way of a condensate valve 415. At the end of the steaming time, the steam outlet valve 414 is opened for pressure drop to atmospheric. Discharge of product 403 through a door 417 in the grid 413 and subsequently through the product outlet port 411 is then effected. There is downstream transfer of product 403 by auger to a brush and belt skin removal arrangement. The necessity for significant numbers of moving parts within the pressurised region, in particular three doors 406, 409 and 417, together with the need for pressure sealing of at least the drive 418 for the agitator 412 by way of a rotary joint or gland leads to a potentially significant maintenance requirement in a system of this kind, as well as high cost in construction.
A further peeling arrangement using a static pressure vessel is shown in FIG. 5, in which product is charged 502 to a basket 519 which is located within a pressurizable region or dome 516. The basket 519 is shown in FIG. 5 in a discharge or dump orientation and reference 502 indicates the direction of charging or loading when the mouth of the basket 519 is directed upwards. The dome 516 is then sealed and charged with steam, while the basket 519 containing the product is rotated or turned within the dome 516, for exposure of the product to steam and immediate run-off of condensation. At the end of the steaming period, a large steam outlet provides for rapid fall in pressure to optimise bursting of the skin. As will be apparent however from the drawing, the region 516 to be charged with steam is of significantly greater volume, to a multiple degree, than the region 519 of this system actually containing product, so that the system of FIG. 5 is somewhat extravagant in its use of steam, while also the ability to secure rapid or flash blow-off of the steam with substantially instantaneous reduction in pressure is reduced, because of the very great volume of steam to be relieved.
FIG. 6 shows a prior art steam peeling system developed by the present inventor, using a rotating pressure vessel 601 and various associated equipment. The vessel 601 is of generally symmetrical cylindrical form about an axis of symmetry, which extends in the plane of the paper, and the vessel 601 is rotatable about a substantially horizontal axis, which, as shown in the drawing, extends perpendicular to the plane of the paper. Product is brought to the steam peeler vessel 601 by way of an in-feed container and is batched in a hopper unit 602 that supplies product through the pressure vessel 601 door opening or mouth 604 when the vessel 601 is oriented in a generally upward disposition. When the vessel 601 is sealed, rotation takes place about the substantially horizontal axis perpendicular to the plane of the paper, without rotation of the pressure vessel 601 about its axis of symmetry, and at the end of the steaming period, the pressure vessel 601 is relieved such as by valve 614 to a large volume exhaust vessel 621, for so-called “rapid flash” or expedited reduction in steam pressure within the pressure vessel 601, thereby engendering effective bursting of the peel from the surface of the product. Charging of the vessel 601 for the steaming period takes place in substantially known manner such as via valve 605 from a steam accumulator 622. Product is discharged from the pressure vessel 601 in a substantially inverted disposition thereof and is then brought by way of a product transfer auger 623 to a centrifugal separator 624, where peel is removed and discharged to waste, while the peeled product is advanced to further food processing operations as may be required.
This system has proved to be effective and economical, subject to certain disadvantageous aspects, according as understanding of the peeling process and the relevance of certain parameters of the operations carried out during peeling has become further understood.
There still remains a need to overcome the disadvantages of prior art peeling systems, and especially steam peeler pressure vessels, as indicated above. It is particularly desirable to provide an improved steam peeler pressure vessel and also to provide an improved feed arrangement for steam peeling pressure vessels. It is further desirable to provide improved arrangements for steam discharge. It is a still further desirable to provide improved arrangements in a steam peeling system for accelerating pressure relief. It is still further desirable to further improve the steam peeler by improving the manner of exhausting steam to atmosphere in a steam peeling system. The present invention addresses the above needs.